It is known from U.S. Pat. No. 4,173,362 to form a pipe joint in a complex mold by first molding a pair of seal rings on a mold core, then by displacing outer mold parts to allow molding of a pipe part around the two seal rings. At the interface between the seal rings and pipe part there will normally be a good bond which will ensure that the pieces remain virtually integral. After some curing the core parts are pulled out of the assembly with appropriate deformation of the fairly soft elastomeric seal rings.
Such an arrangement does indeed form an excellent joint assembly. Nonetheless it is essential that the thus formed joint be in at least one axial direction of sufficiently large diameter that the core parts can be extracted. Furthermore as the core parts are extracted with deformation of the seal rings, it is essential to wait until the seal rings are fully cured; otherwise withdrawal of the core part will permanently deform the seal ring. Another disadvantage of this system is that the bond between the seal ring and the pipe releases, allowing the seal ring to slip out of the pipe.